Ferrimagnetism

Based on the presence of permanent dipoles and their orientations magnetic materials are classified into five categories. Magnetism arises due to several aspects. Mainly we have permanent magnetic materials and non-permanent permanent magnetic materials. Ferrimagnetism is one of the permanent magnetism i.e., the materials will possess the permanent dipole orientations.

Ferrimagnetism is a type of permanent magnetism that happens in solids during which the magnetic fields related to individual atoms spontaneously align themselves, some parallel, or within the same direction (identical to ferromagnetism), et al. generally antiparallel, or paired off in opposite directions ( similar to antiferromagnetism).

Ferrimagnetic Material:

Ferrimagnetism is an idea that was originally proposed to the world by Néel to describe the magnetic ordering phenomena in ferrites, in which Fe ions appear in two different ionic states and hence experience different magnetic moments with mutual antiferromagnetic coupling. The ferromagnet can be considered in a loose analogy as a two-sublattice antiferromagnet with 丨M\[_{A}\]丨≠丨M\[_{B}\]丨. In this context of magnetic properties of the materials, ferrimagnets appear sometimes in the literature under the name uncompensated antiferromagnet.

As a consequence, a net spontaneous magnetization is observed at temperatures below the ordering temperature T\[_{C}\]. different forms of M\[_{S}\](T) curves are found for ferrimagnets depending on the temperature variation of sublattice magnetizations.

The ferrimagnetic effect is observed when the magnetic moments of the domains in the substance are aligned in parallel and antiparallel directions such that they are not equal in numbers. Ferrimagnetic substances or particles are weakly attracted by a magnetic flux as compared to ferromagnetic substances.

The ferrimagnets are also corresponded to antiferromagnets, in that the exchange coupling between adjacent magnetic ions leads to antiparallel alignment of the localized moments. So, entire magnetization occurs because the magnetization of one sublattice is greater than that of the oppositely oriented sublattice.

The observed ferrimagnetic susceptibility and the magnetization of ferrimagnets can be reproduced using the Weiss molecular theory or Weiss molecular field theory. The localized-moment model applies very well to ferrimagnetic materials since most are ionic solids with largely localized electrons.

Ferrimagnetic Materials:

Ferrimagnetism occurs chiefly in magnetic oxides referred to as ferrites. Natural magnetism is generally observed by lodestones, recorded as early because the 6th century BC is that of ferrite, the mineral magnetite, a compound containing negative oxygen ions O\[^{2-}\] and positive iron ions in two states, iron(II) ions, Fe\[^{2+}\], Fe\[^{3+}\]. The oxygen ions aren't magnetic, but both iron ions are. 

Did You know:

Ferrites are considered to be of high importance in engineering and technology because they possess a spontaneous moment of a magnet below the Curie temperature just an iron, cobalt, Nickel. Because of the very low eddy current losses, ferrites are used as a core of coils in microwave frequency devices and memory core elements. Due to relatively low permeability and flux density compared to iron, ferrites are not suitable for use in the high field and high power applications, such as motors, generators and power transformers, but they can be used in low field and low power applications.